1. Field of the Invention
The invention relates to an image forming apparatus that forms characters and images on a predetermined recording medium by fixing toner thereto.
2. Description of Related Art
Generally, an image forming apparatus forming characters and images on a predetermined recording medium by fixing toner thereto performs following steps to form an image. First, the image forming apparatus forms an electrostatic latent image on a surface of a photosensitive drum serving as an image holder with an exposure device such as LED (Light Emitting Diode) head and the like. Then, the formed electrostatic latent image is developed with toner including colorant, and the obtained visible image is transferred to a recording medium such as recording paper and the like. Thus, the image is formed on the recording medium.
To develop the electrostatic latent image with the toner including colorant, the image forming apparatus has a developing roller for attaching the toner to the electrostatic latent image formed on the photosensitive drum and a toner supply roller for supplying the toner to the developing roller. A potential difference between the toner supply roller and the developing roller causes charged toner to be supplied from the toner supply roller to the developing roller at a contacting portion formed by the toner supply roller and the developing roller overlapping with each other (this portion is hereinafter referred to as a NIP portion pushing depth).
For example, both of the toner supply roller and the developing roller are secured, and an axial distance between the toner supply roller and the developing roller is configured as a constant interval, as disclosed in Japanese Patent Application Publication No. 2002-108089.